Although they can be applied to any fibre composite structures, the present invention and the problems on which it is based will be described in more detail in relation to a carbon- fibre-reinforced plastics material components (CFRP) of an aircraft structure.
Aircraft components are increasingly being produced, for weight-saving reasons, from fibre composite materials, in particular from carbon-fibre-reinforced plastics material (CFRP). In this case, they have a structure of a plurality of layers of fibre interlaid scrims, which are connected to one another by means of a cured resin matrix, in particular epoxy resin. To produce components of this type, in conventional methods, fibre interlaid scrims impregnated with a resin matrix (in particular epoxy resin) are placed in a plurality of layers in a laminating device. The resin matrix is then cured, for example under the action of elevated temperature and elevated pressure.
According to a conventional method, a component is enclosed for curing in a sack made of pressure-tight film, the interior of which is evacuated by means of a vacuum pump. The component enclosed in this manner is then placed in an autoclave, where it is subjected to elevated pressure.
If reworking operations, such as, the correction of faults, repair of damage and/or modification of components are to be carried out on fibre composite components of this type, in a conventional machining method, for example, preimpregnated fibre layers (prepregs) are fixed using an adhesive film on the surface of the component to be machined and covered with a pressure-tight diaphragm, for example a vacuum sack. The region enclosed under the diaphragm is evacuated. As the required curing pressure is often more than 1 bar, this vacuum sack method cannot be used alone. For this purpose, the component is placed in an autoclave, where it is subjected to elevated pressure to cure the fibre layers.
Therefore, a suitable adhesive device is generally required to receive and support the component to be machined. Alternatively, clamping mechanisms to mechanically apply pressure can also be used.
DE 10 2007 026 099 A1 discloses a device and a method for machining a fibre composite structure, a pressure-tight hood-type mat with the introduction of an excess pressure being disclosed.
During reworking operations on fibre composite components, it is often also necessary to rework not only level faces, but also, for example, reinforcement profiles, for example stringers (i.e. to remove faulty laminate and replace it with a new laminate made of the same material and with the same layer structure).
It is felt to be disadvantageous in this case that additional capacity in the autoclave and in the original adhesive devices leads to extra costs and a loss of time.
Mechanical clamping mechanisms can often only produce a non-uniform pressure distribution and this results in pores and thickness fluctuations. Faulty reworking therefore has to be repeated. When using a pressure-tight hood-type mat, there may be the risk of inadequate stability.
It is therefore one object of the present invention to provide an improved method for at least partially reworking or replacing a reinforcement element of a fibre composite structure, which makes it possible to connect fibre layers for reworking and/or as a replacement in the case of high material quality and precision, without using an autoclave, to the fibre composite structure.